Diesel engines are the prime workhorses of global transport and agriculture sectors. However, they emit significantly higher quantities of oxides of nitrogen (NOx) and particulate matter (PM). This unique study involves evaluation of in-situ spatial distribution of temperature and soot in the engine combustion chamber using high-temperature endoscopy, while the engine was being fuelled with emerging fuels so that suitable strategies for effective control of emissions could be devised. Two new test fuels namely diesosene (K20) (20% kerosene (v/v) blended with mineral diesel) and diesoline (G20) (20% gasoline (v/v) blended with mineral diesel) were compared with the baseline mineral diesel in a conventional direct injection compression ignition (DICI) engine. These two fuels represent relatively inferior quality diesel, which is increasingly available in global markets due to gradually exhausting petroleum resources and is produced from heavier/residual crude left in the oil wells. Diesoline showed superior combustion characteristics compared to diesel and diesosene. Endoscopic visualization technique emerged to be an effective tool, wherein real-time combustion characteristics of various test fuels could be successfully evaluated in a time efficient and cost-effective manner. This research article shows the experimental implementation of an emerging optical technique, which might be potentially useful in designing more efficient engines in quicker turn-around time for research and development.